Polarity sensitive electronic switch and polarity indicator

ABSTRACT

A solid state switch for performing a control operation which is operated by a voltage of a particular polarity and a diode and indicating means connected in series across the switch. The diode and indicating means are connected in series across the switch so that current flows through the diode and the indicating means in response to the application of a voltage of incorrect polarity to the switch means. Flow of current through the indicating means causes it to signal the application of a voltage of incorrect polarity.

United States Patent Norman [4 Feb. 5, 1974 [75] Inventor: William L. Norman, Sylmar, Calif.

[73] Assignee: Norman Enterprises, Inc., Burbank,

Calif.

[22] Filed: May 19, 1972 [21] Appl. No.: 255,141

[52] US. Cl 250/211 J, 317/43, 324/133, 307/311 [51] Int. Cl. HOlj 39/12 [58] Field of Search 324/133; 317/43, 31; 250/211 .1, 211; 307/127, 311, 202

[ 56] References Cited UNITED STATES PATENTS 3,355,600 11/1967 Mapham 307/311 3,267,301 8/1966 Gignac 307/127 3,475,617 10/1969 Chaimowicz.. 250/211 .1 2,956,229 10/1960 l-lenel 324/133 3,079,532 2/1963 Segrest 317/31 3,051,887 8/1962 Lind 307/127 3,417,253 12/1968 Kadah et a1 250/211 J FOREIGN PATENTS OR APPLICATIONS 950,456 2/1964 Great Britain 324/133 OTHER PUBLICATIONS Compensating Amplifier by Vonfeldt, IBM Technical Disclosure Bulletin, Vol. 11, No. 2, p. 131 July 1968.

Light Activated Switch by Howell, Electronics, Vol. 37, No. 15, May 4, 1964, pages 5355.

Primary Examiner-James W. Lawrence Assistant Examiner-Harold A. Dixon [5 7] ABSTRACT A solid state switch for performing a control operation which is operated by a voltage of a particular polarity and a diode and indicating means connected in series across the switch. The diode and indicating means are connected in series across the switch so that current flows through the diode and the indicating means in response to the application of a voltage of incorrect polarity to the switch means. Flow of current through the indicating means causes it to signal the application of a voltage of incorrect polarity.

1 Claim, 4 Drawing Figures POLARITY SENSITIVE ELECTRONIC SWITCH AND POLARITY INDICATOR BACKGROUND OF THE INVENTION Thisdevice pertains to the art of building solid state switching devices which only operate on application of a voltage of a predetermined polarity and, more particularly, to the art of building light activated switching devices which trigger a remote electronic flash unit in response to light from a master flash unit. If prior art devices such as the devices described in U. S. Pat. Nos. 3,209,154; 3,313,939; 3,424,908 and 3,487,221, for example, are utilized as a trigger device for firing a remote electronic flash unit, it is necessary to apply a voltage of the proper polarity to the solid state switching device. Since the connector in commercial flash units for presenting a voltage to a trigger device is commonly an ordinary AC receptacle, the operator must determine the polarity of the voltage in order to be certain that the trigger device will operate properly. The polarity of the voltage presented by the remote flash unit is usually determined by operating a master flash unit and observing if the remote flash unit also operates. Such devices are subject to the disadvantages that the type of event to be photographed may make it desirable to minimize the number of flashes of light from photographic equipment and it may not be convenient or possible for the operator to travel to and from the remote flash unit. In addition, typical switch devices such as SCR circuits are extremely sensitive to an extent that, where such a circuit is incorrectly connected to a voltage source, it will sometimes operate. Thus, even a test of a piror art device may not be reliable.

SUMMARY OF THE INVENTION According to the concepts of the invention, a solid state switch which only operates on a voltage of a predetermined polarity is connected to a pair of terminals. The terminals are adapted for receiving a DC voltage from a triggering source. A diode and an indicating means are connected in series across the switching means. The diode is connected so that a current will flow through it in response to the application of a voltage of incorrect polarity to the switching device. That is, the diode will conduct when the switching device cannot and vice versa. The flow of current through the diode also flows through the indicating means which signals the application of a voltage to the switching means of incorrect polarity. The polarity of the applied voltage may then be reversed for proper operation of the switch. In the preferred embodiments the indicating means is a neon glow lamp and the swwtch is a silicon controlled rectifier activated by one or more photovoltaic cells for triggering a remote device in response to a flash of light from a master device. If the triggering device is plugged into a remote device such as an electronic slave flash unit so that the voltage of the wrong polarity is applied to the silicon controlled rectifier, the neon lamp lights to indicate this. The trigger device may then be reversed in the receptacle in the slave unit. The operator is thus assured that the-trigger device is ready to operate without performing any further tests to determine polarity.

It is therefore an object of the invention to provide a switching circuit which operates on a voltage of a pre' determined polarity and which gives a signal when a voltage of the incorrect polarity is applied to the circuit.

It is another object of the invention to provide a silicon controlled rectifier circuit which operates on a voltage of a particular polarity and which presents a visual indication upon application of a voltage of incorrect polarity to the recitifer.

DESCRIPTION OF THE DRAWINGS FIGS. 1, 2 and 3 are schematic diagrams of several embodiments of the invention.

FIG. 4 is a perspective view of the preferred embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1 there is shown an embodiment of the invention utilizing a silicon controlled recitifer. A pair of terminals 10 and 12 receive a DC voltage. For the embodiment of FIG. 1 this DC voltage may be in the range from to 300 volts presented by a high impedance source in an electronic flash unit. In the usual application the connector is symmetrical which may result in the application of either a positive or a negative voltage to terminal 10 and either a positive or a negative voltage to terminal 12. Silicon controlled rectifier 14 is a semiconductor device which requires the application of a voltage of a proper polarity in order to function. In order for silicon controlled rectifier 14 to function, a negative voltage must be applied to its cathode and a more positive voltage applied to its anode. This means that the polarity of the voltages applied to terminals 10 and 12 must be a positive voltage applied to terminal 12 and a more negative voltage applied to terminal 10. The silicon controlled recitifer will notconduct until it is triggered by the application of a positive electrical signal at the gate terminal. Once the rectifier conducts in the forward direction, the gate current no longer has any control, and the rectifier behaves as a low-forward-resistance diode. The gate regains control when the current through the rectifier is cut off.

The gate current into the silicon controlled rectifier 14 is generated by a photo voltaic cell or solar cell 16 which is coupled to the gate of silicon controlled rectifier 14 through capacitor 18 and resistor 20. A voltage generated'by one or more solar cells 16 charges capacitor 18 through the gate terminal of silicon controlled rectifier 14, supplying the current that triggers it into forward condition. Resistor 20 is a bleeder resistor for discharging capacitor 18. The device of FIG. 1 may be used to trigger a slave flash unit in response to a flash of light from a master flash unit. Capacitor 18 and resistor 20 prevent a trigger in response to more gradual variations in intensity of light infringing upon solar cell 16 from sources such as flood lamps, interior lighting and the sun. Once silicon controlled recitifer 14 conducts, it will continue to conduct until the voltage across terminals 10 and 12 is either removed or decreases to a value which will not sustain conduction. However, if a positive voltage is applied to terminal 10 and a more negative voltage to terminal 12, silicon controlled rectifier 14 will be reversed biased and will not conduct in response to a trigger voltage from capacitor 18.

In accordance with the invention a diode 22 and a neon lamp 24 are connected in series across the anode and cathode of silicon controlled rectifier 14. The anode of diode 22 is connected to the cathode of silicon controlled rectifier 14. The application of a voltage across silicon controlled rectifier 14 which is of the incorrect polarity for conduction will be indicated by lamp 24. Diode 22 is connected so that current flows through it upon the application of a voltage to terminals 10 and 12 and hence to the anode and cathode of silicon controlled rectifier 14 which is incorrect for obtaining conduction through the rectifier.

Turning now to FIG. 2, there is shown another embodiment of the invention utilizing diode 22, indicating lamp 24 and a light activated silicon controlled rectifier 26. Rectifier 26 is a silicon controlled rectifier such as a GE type L8B which includes a glass window for passing incident light to a photo voltaic cell mounted inside the housing. The photo voltaic cell operates the switch in response to a predetermined amount of incident light. However, rectifier 26 also requires the application of the proper polarity voltage to function. In this embodiment diode 22 and indicating lamp 24 are connected in series across the rectifier 26. Diode 22 is connected with the polarity such that the application of a voltage of the wrong polarity to rectifier 26 will cause current to flow through diode 26 and through indicating lamp 24. Illumination ofindicating lamp 24 thus indicates that the wrong polarity voltage has been applied to rectifier 26. Resistor 28 controls the firing sensitivity, i.e., the amount of light required to trigger rectifier 26.

Consider now the embodiment of FIG. 3. In this embodiment diode 22 and indicating lamp 24 are connected in series across transistor 30. As in the embodiments of FIGS. 1 and 2, diode 22 is connected with the polarity such that the application of the wrong polarity voltage to transistor 30 will cause current to flow through diode 22 and indicating lamp 24. The illumination of indicating lamp 24 will thus indicate that the wrong polarity of voltage has been applied to the device. For the device of FIG. 3, a positive voltage must be applied to the collector of transistor 30 and a more negative voltage to the emitter.

Any one of the embodiments shown in FIGS. 1, 2 and 3 may be fabricated as a plug adapted to fit a standard electrical recepticle as illustrated in FIG. 4. Terminals 10 and 12 comprise a pair of prongs projecting from the plug. The components are potted in a housing 36 which is a transparent material for passing light to solar cell 16. Housing 36 may also be fabricated ofa resilient transparent material so that the device is capable of sustaining shocks from being dropped without damage. Housing 36 may be formed from Chemical Products Corp. No. PK6650 urethane resin and R8310 hardener.

The operation of the devices shown in FIGS. 1, 2 and 3 is evident from the above discussion. Assume that a voltage is applied to the switch, silicon controlled rectifier 14 in FIG. 1, light activated silicon controlled rectifier 26 in FIG. 2, or transistor 30 of FIG. 3, and that this voltage is of incorrect polarity for the switch means to function. For the switch shown in FIGS. 1, 2 and 3 this would mean a positive voltage on terminal 10 and a more negative voltage on terminal 12. This positive voltage is also applied to the anode of diode 22 which in turn causes current to flow through diode 22 and indicating lamp 24. Indicating lamp 24 illuminates to indicate the application of a voltage of incorrect polarity to the switch. The polarity of the voltage on terminals 10 and 12 must then be reversed. For a light activated trigger unit as shown in FIG. 4 reversal of the polarity 5 of the voltage is accomplished by merely removing the plug from the recepticle and reinserting the prongs in the opposite connector holes of the recepticle in the device applying the voltage (not shown) Reversal of the polarity of the voltage to terminals and 12 extinguishes indicating lamp 24 because current flow is blocked by diode 22. The device is then ready for operation. The switching means will conduct in response to a voltage generated by solar cell 16 whenever the incident light on solar cell 16 reaches a significant intensity in a given amount of time. Conduction through the switching means of FIGS. 1, 2 and 3 electrically connects terminals 10 and 12. In the intended application of the devices of FIGS. 1, 2 and 3 the shorting together of terminals 10 and 12 would trigger the operation of a remote flash unit.

It should be understood that the scope of the invention is not limited by the drawings and description of the preferred embodiments and that other embodiments and modifications may be made without departing from the scope of the invention as claimed. Although the switches of FIGS. 1, 2 and 3 operate to short terminals 10 and 12 together, other control operations such as starting a counter or closing a relay, for example, could be performed.

What is claimed is:

l. A switching device responsive to a flash of light comprising:

a a pair of terminals for selectively receiving a DC voltage;

b at least one photovoltaic cell for generating age in response to light;

0 a silicon controlled rectifier for switching a voltage,

said silicon controlled rectifier having anode, cathode and gate electrodes, said anode electrode coupled to one of said terminals, and said cathode electrode coupled to the other of said terminals, said gate coupled to said photovoltaic cell, said silicon controlled rectifier conducting in response to the application of a voltage having a first polarity to said anode and cathode electrodes and to a voltage received at said gate electrode from said photovoltaic cell;

d a circuit comprising a diode and a light-emitting means connected in series between said terminals, said diode connected to conduct in response to a DC voltage of a second polarity opposite to said first polarity, said light-emitting means signaling whenever said diode means conducts to indicate the application of the voltage of said second polarity to said anode and cathode electrodes;

e a resistor and a capacitor in parallel for coupling a voltage generated by'said photovoltaic cell to said gate, said silicon control rectifier conducting only in response to a flash of light received by said photovoltaic cell; and

f a transparent resilient material encasing said photovoltaic cell, said rectifier, said circuit and said resistor and capacitor. 65 4:

a volt- 

1. A switching device responsive to a flash of light comprising: a a pair of terminals for selectively receiving a DC voltage; b at least one photovoltaic cell for generating a voltage in response to light; c a silicon controlled rectifier for switching a voltage, said silicon controlled rectifier having anode, cathode and gate electrodes, said anode electrode coupled to one of said terminals, and said cathode electrode coupled to the other of said terminals, said gate coupled to said photovoltaic cell, said silicon controlled rectifier conducting in response to the application of a voltage having a first polarity to said anode and cathode electrodes and to a voltage received at said gate electrode from said photovoltaic cell; d a circuit comprising a diode and a light-emitting means connected in series between said terminals, said diode connected to conduct in response to a DC voltage of a second polarity opposite to said first polarity, said light-emitting means signaling whenever said diode means conducts to indicate the application of the voltage of said second polarity to said anode and cathode electrodes; e a resistor and a capacitor in parallel for coupling a voltage generated by said photovoltaic cell to said gate, said silicon control rectifier conducting only in response to a flash of light received by said photovoltaic cell; and f a transparent resilient material encasing said photovoltaic cell, said rectifier, said circuit and said resistor and capacitor. 